抄録
The coprecipitation of various amino acids (phenylalanine: Phe, alanine: Ala, leucine: Leu, tryptophan: Trp, histidine: His and aspartic acid: Asp) into the Zn-Al layered double hydroxide (LDH) was quantitatively investigated at 40°C. When Phe was used as a guest amino acid, the coprecipitation was influenced by the solution pH, Zn/Al/Phe molar ratio and kind of coexisting inorganic ion. The optimum conditions were reaction time: 1h, pH range: 7-9 and Zn/A1/Phe molar ratio: 2-4/0.5-1/1, in which Phe was thought to be intercalated into the Zn-Al LDH precipitates as zwitterion. In the (Cl, Phe)/Zn-Al LDH and Phe/Zn-Al LDH precipitates, the basal spacing of (003) was observed at 7.8Å(using chloride reagent) and 18.8Å(using nitrate reagent), respectively. It suggests that the intercalated Phe was oriented horizontally or vertically for the Zn-Al LDH basal layer, in which the arrangement was dependent on the charge density of coexisting inorganic ions. In the case of various other amino acids, the coprecipitation greatly influenced by the kind of side-chain of the amino acids. The amino acids having hydrophobic side-chain (Leu and Trp) were preferentially intercalated into the LDH interlayer as zwitterion. Moreover, in the deintercalation experiments of Phe from the Phe/Zn-Al LDH precipitate, Phe was easily deintercalated by the ion exchange with CO32- ion.
